Added new API routine to get TCP stats.
Ensure uhi_realloc() does not free the memory when size is zero, to
match the kernel realloc() behavior.  Host OS realloc(,0) behavior
varies.
uinet_malloc() now implements M_WAITOK.
Gate temporary passive debug traces with a sysctl.
Become much more silent when no verbose flag is given.  Print tcp stats every two seconds.
Disable syncookies for passive connections.
Increase syncache size.
- Improved pcap and netmap interface statistics collection.

- Added uinet_getifstat() to UINET API to retrieve interface statistics.

- bin/passive now prints interface stats every two seconds.
Fixed a bug in ev_uinet_stop().  If ev_uinet_stop() was called on a
watcher that was being processed in the current event loop iteration,
and that watcher was the last remaining watcher for the corresponding
socket context, that socket context was not being removed from the
previous-pending list.

This could result in one or more of: upcalls being re-enabled for the
corresponding socket, access to and/or corruption of freed memory,
corruption of the pending list.

Also made a cosmetic change of a call to free() to ev_free().
Fix memory leak.
Merge branch 'passive_receive' of github.com:pkelsey/libuinet into passive_receive_adrian

Conflicts:
	bin/passive/passive.c
Fix merge.
Make the sysctl debugging configurable.
Migrate the single define that we're currently using into
the .h so it can be used by the userland code.